DESCRIPTION: (Applicant's Abstract) This proposal concerns the impact of comorbid drug abuse and mental disorders on individuals and service systems. Using a longitudinal design, this study will contrast two samples of comorbid adults recruited during an acute care episode in county service systems. One sample will be drawn from the substance abuse treatment system (n=125), and one will be drawn from the mental health treatment system (n=125). To control for differences not related to comorbidity, an equal number of non-comorbid subjects will be recruited, bringing the sample total to 500 subjects, 250 from substance abuse and 250 from mental health treatment. Data on key demographic and severity of alcohol and drug use variables will be obtained at treatment entry, and a diagnostic assessment will be performed. Psychosocial data on alcohol and drug use, risk factors for HIV/AIDS, prevalence of violence, and quality of life will be obtained for a prospective 24 month community follow-up period. Service use and cost data will be obtained from substance abuse, mental health, public health, and forensic services for a period of 24 months prospectively and 24 months retrospectively from time of recruitment. We will test the null hypothesis that the two samples are from the same population on key entry variables. The samples will also be contrasted on the psychosocial, service use, and cost variables. If the samples are found to be from the same population on key entry variables, then differences in psychosocial status, service use, and costs will suggest differences in treatment service systems rather than differences between the clients of these systems. If the samples are significantly different on key entry variables, it will imply the presence of unique comorbid groups. Both similarities and differences between the two samples will be of utmost value. Findings that the comorbid samples are from the same population can guide coordination or integration of services. Findings that they are from different populations can lead to increased precision in distinguishing types of comorbid disorders in treatment systems and should enhance development of services, tailored to the needs of unique comorbid groups.